At the posted coordinates you will be at the tail waters of an artificial creek in the harbor area. Along the creek are metal plaques embedded in the ground. Search the plaques for clues to the final at :
N39 17.1ZX W84 23.348
Find plaque #11 - has a starfish on it
The brachipod shown is 3 - X/Y inches
"....ian period - 345 to 40Z million years ago."
Sum check = X+Z = 6